1. Field of the Invention
This invention relates to rotating planar array antennas, and more particularly, to an antenna construction able to obtain a high data rate.
2. Description of the Prior Art
Prior art radar systems have employed two-dimensional scanning, i.e., scanning in elevation and azimuth to obtain the desired scan coverage. For example, U.S. Pat. No. 3,434,139 issued Mar. 9, 1969 to J. A. Algeo, and U.S. Pat. No. 3,518,689 issued June 30, 1970 to J. A. Algeo et al, both assigned to North American Rockwell Corporation, disclose radar systems employing a serpentine feed for each row of radiating elements and a serpentine feed for each column of radiating elements arranged in a linear array. A two-dimensional scan is achieved by controlling the frequency of the inputs to the two serpentine feeds. This feed structure results in a heavy, bulky construction and provides only a single unambiguous beam, which limits the data rate for the antenna system. In another prior art system disclosed in U.S. Pat. No. 4,041,501, issued Aug. 9, 1977 to Frazita et al and assigned to Hazeltine Corporation, a plurality of phase shifters is employed to provide an output signal having a desired wave form. This array configuration uses a plurality of feed elements connected to the antenna elements by directional couplers to produce a single unambiguous beam, which limits the maximum available data rate.
For edge slotted waveguide rows in a conventional single beam antenna, the slot spacing is approximately one-half the guide wavelength, and the slots are alternately tilted in opposite directions relative to the antenna centerline. This introduces a 180 degree phase compensation and steers the beam close to broadside. However, it also means that the cross-polarization (vertical) components alternate in phase relative to the principal polarization (horizontal) components. The result is that cross-polarization lobes peak up off axis on the diagonal planes, resulting in a substantial peak sidelobe.